Dispersible adhesively bonded tissue laminate

ABSTRACT

Disclosed is a dispersible adhesively bonded wet tissue laminate and more particularly a dispersible wet wipe comprising two or more adhesively bonded tissue plies. Generally, the wipe comprises first, and second tissue plies adhesively bonded to one another by an adhesive, particularly a triggerable binder, disposed at the interface of the plies. The first and second tissue plies preferably comprise fibrous tissue plies and more preferably wet-laid tissue plies consisting essentially of conventional papermaking fibers. The adhesively bonded laminates are generally strong enough to withstand use, such as having a geometric mean wet tensile strength (GMWT) greater than about 250 g/in, but disperse quickly in water, such as having a Slosh Time less than about 60 minutes.

BACKGROUND

Pre-moistened wipes are popular in the marketplace, including, forexample, baby wipes, toddler wipes, surface cleaning wipes, femininewipes, hemorrhoid wipes, make-up removal wipes, and child and adulttoileting wipes. Consumers flush many of these wipes down the toilet.Some of the wipes are designed to be flushed and labeled as such. It isimportant that wipes that are intended to be flushed are compatible withsewer and septic systems, but also important that such wipes do not fallapart when used for their intended purpose. Specifically, when aflushable disposable product is flushed down a toilet into sewer orseptic systems, the product, or designated portions of the product,should degrade or lose strength as it moves through various steps ofwastewater processing.

One common approach to making a flushable wet wipe is using“hydroentangling” technology, in which fibers, primarily or exclusivelycellulosic fibers, are “entangled” together using very smallhigh-pressure water jets. However, some wipes made with this technologyrequire a substantial amount of agitation to break apart after flushing,and some wipes, if made to have a very high initial strength, may notlose significant strength in relatively static environments.

Another conventional approach to making a wet wipe that exhibitssatisfactory in-use strength, but that adequately breaks down in seweror septic systems, is via the use of a binder on a substrate comprisingcellulose fibers. The binder attaches to cellulose fibers, and bondsthose fibers together in a network to deliver in-use strength. Thebinder is stable and delivers this strength when soaking in astabilizing solution but swells and weakens in the tap water of thetoilet and sewer system, thus allowing the fiber network to break apart.The strength of the wipe can be manipulated by varying the amount ofbinder used and the process conditions by which the binder is applied,such as how and when it is applied to the wipe substrate, and by varyingthe time and temperature at which the binder is dried/cured.

One variant of such a binder/stabilizing solution is a salt-sensitivetriggerable binder, such as that disclosed in U.S. Pat. No. 6,994,865.The binder holds the fibers of the wet wipe together when soaked in asalt solution, which stabilizes the binder. When the salt solution iswashed away, the binder swells and fails, and the wipes lose strength.However, such binders can be relatively expensive, and it can bechallenging to achieve the right balance of in-use strength andpost-flush degradation when using such binders. For example, the binderadd-on level can be reduced to improve dispersibility and reduce cost,but in-use strength (during toileting) can suffer. Conversely, thebinder add-on can be increased to improve in-use performance (duringtoileting), but dispersibility can suffer, and cost increases.

What is needed is a cellulose-based wipe that combines sufficient in-usestrength, adequate strength loss after flushing even in relativelynon-turbulent water, and that is cost-effective.

SUMMARY

The present invention provides a dispersible adhesively bonded wettissue laminate and more particularly a dispersible mutli-ply wet tissueproduct comprising a first wet-laid tissue ply and a second wet-laidtissue ply adhered to one another by an adhesive and more specifically atriggerable binder. Generally, the triggerable binder is disposedbetween the plies to adhere them to one another. The triggerable bindermay be applied to an outer surface of one, or both of, the wet-laidtissue plies prior to passing the plies through a nip, followed bycuring of the binder. In this manner, the wet tissue products of thepresent invention may comprise outer surfaces that are substantiallyfree from a triggerable binder but have a triggerable binder disposed onthe interior along the interface of the two layers. Selectivelydisposing the adhesive between layers adheres the layers together toprovide sufficient strength in use but facilitate break-up when theproduct is flushed.

Accordingly, in certain embodiments, the present invention provides adispersible adhesively bonded wet tissue laminate comprising a firstwet-laid tissue ply and a second wet-laid tissue ply arranged in facingrelation to one another and a triggerable binder disposed there between.In certain instances, it may be preferable that each of the wet-laidtissue plies be similarly manufactured. For example, both plies may bethrough-air dried tissue plies. In still other instances, it may bedesirable that each of the wet-laid tissue plies be structurally similarto one another such as, for example, having a similar furnishcomposition, basis weight, sheet bulk, or geometric mean tensilestrength.

In other embodiments the invention provides a dispersible adhesivelybonded wet tissue laminate comprising: a first tissue ply and a secondtissue ply, each ply having a first outer surface and a second outersurface, the first and second plies arranged in facing relation with oneanother such that the second outer surfaces face one another; anadhesive disposed between the first and second tissue ply second outersurfaces. The adhesively bonded tissue laminate further comprises awetting composition, particularly an aqueous wetting compositioncomprising an insolubilizing agent such as a salt.

In a particularly preferred embodiment, the tissue products of thepresent invention are provided in a wet format, i.e., they contain awetting composition added to a dry tissue laminate at add-ons rangingfrom about 10 to about 600 percent, based upon the weight of the drytissue laminate. Despite being wet, the products are relatively strong,such as having s a geometric mean wet tensile strength (GMWT) greaterthan about 250 Win, yet are readily dispersed when flushed, such ashaving a Slosh Time less than about 60 minutes.

In still other embodiments a dispersible adhesively bonded wet tissuelaminate comprising: a first through-air dried tissue ply having a basisweight from about 15 to about 35 gsm and a second through-air driedtissue ply having a basis weight from about 15 to about 35 gsm, each plyhaving a first and a second outer surface, the first and second pliesarranged in facing relation with one another such that the second outersurfaces face one another; a cationic polyacrylate adhesive and acobinder selected from the group consisting of poly(ethylene-vinylacetate), poly(styrene-butadiene), poly(styrene-acrylic), a vinylacrylic terpolymer, a polyester latex, an acrylic emulsion latex,polyvinyl chloride), ethylene-vinyl chloride copolymer and acarboxylated vinyl acetate latex, disposed between the first and secondtissue ply second outer surfaces, wherein the add-on of adhesive andcobinder ranges from about 3 to about 10 grams per square meter oftissue laminate.

In yet other embodiments a method of making a dispersible adhesivelybonded wet tissue laminate: (a) providing a first wet-laid tissue webhaving a first surface and a second surface; (b) providing a secondwet-laid tissue web having a first surface and a second surface; (c)applying an adhesive to the first surface of the first wet-laid tissueweb; (d) after applying the adhesive to the first surface bringing thefirst surface into facing relation with the first surface of the secondwet-laid tissue web; (e) passing the first and second wet-laid tissuewebs through a nip to form and adhesively bonded wet tissue laminate and(f) applying a wetting composition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a two-ply dispersible wet wipe of the presentinvention;

FIG. 2 is a cross-sectional view of a dispersible wet wipe of thepresent invention with its thickness exaggerated to show detail;

FIG. 3 is an adhesive pattern useful in preparing a dispersible wet wipeaccording to one embodiment of the present invention;

FIG. 4 is another adhesive pattern useful in preparing a dispersible wetwipe according to one embodiment of the present invention.

FIG. 5 is a schematic view of a process for manufacturing a dispersiblewet wipe according to one embodiment of the present invention;

FIG. 6 is a schematic view of a process for manufacturing a dispersiblewet wipe according to another embodiment of the present invention; and

FIG. 7 is a schematic view of a process for manufacturing a dispersiblewet wipe according to yet another embodiment of the present invention.

DEFINITIONS

As used herein the term “machine direction” or “MD” generally refers tothe direction in which a tissue web or product is produced. The term“cross-machine direction” or “CD” refers to the direction perpendicularto the machine direction.

As used herein, the term “basis weight” generally refers to the bone-dryweight per unit area of a product, such as a tissue ply or an adhesivelybonded tissue laminate comprising two or more tissue plies. Basis Weightis generally expressed as grams per square meter (gsm). Basis weight ismeasured using TAPPI test method T-220.

As used herein, the term “ply” refers to a discrete product element.Individual plies may be arranged in juxtaposition to each other. Theterm may refer to a plurality of web-like components such as in anadhesively bonded tissue laminate, which may comprise two, three, fouror more individual plies arranged in juxtaposition to each other whereone or more plies may be attached to one another such as by an adhesive.

As used herein, the term “layer” refers to a plurality of strata offibers, chemical treatments, or the like, within a given ply.

As used herein the term “wet-laid tissue web” generally refers to atissue web that has been manufactured by forming an aqueous suspensionof papermaking fibers, depositing the aqueous suspension on atravelling, water pervious, forming fabric to form a fibrous web anddraining water through the fabric to partially dewater the fibrous web.

As used herein the term “adhesive” generally refers to a compositioncomprising a triggerable binder. In certain non-limiting embodiments,the triggerable binders may comprise the polymerization product of avinyl-functional cationic monomer, a hydrophobic vinyl monomer with amethyl side chain, and one or more hydrophobic vinyl monomers with alkylside chains of 1 to 4 carbon atoms, such as disclosed in U.S. Pat. No.7,157,389, the contents of which are incorporated herein in a mannerconsistent with the present disclosure. In certain instances, theadhesive may comprise a triggerable binder and a cobinder such as, forexample, a vinyl-acetate ethylene latex.

As used herein the term “triggerable binder” generally refers acomposition capable of adhering two tissue plies together to create alaminate according to the present invention that is insoluble in awetting composition comprising an insolubilizing agent but isdispersible or soluble in disposal water such as that found in thetoilet tank, toilet bowl, or waste water system. In certain instancesthe triggerable binder may be a “salt triggerable binder” that isinsoluble in a wetting composition comprising a predeterminedconcentration of sodium chloride, sodium sulfate, sodium citrate,potassium, or other mono or divalent salt acting as the insolubilizingagent, but is dispersible or soluble in disposal water such as thatfound in the toilet tank, toilet bowl, or waste water system.

DETAILED DESCRIPTION

The present disclosure generally relates to water dispersible adhesivelybonded wet tissue laminates and more particularly dispersible wet wipescomprising two or more adhesively bonded tissue plies. In particularembodiments, such as that illustrated in FIG. 1 , a wipe 10 comprisesfirst and second tissue plies 20, 30 adhesively bonded to one another byan adhesive 40 disposed at the interface 50 of the plies. The first andsecond tissue plies 20, 30 preferably comprise fibrous tissue plies andmore preferably wet-laid tissue plies consisting essentially ofconventional papermaking fibers 60.

Conventional papermaking fibers include, for example, wood and non-woodcellulosic fibers, including both bleached and unbleached fibers, virginand recovered or recycled fibers. Particularly preferred papermakingfibers include hardwood and softwood fibers that have been mechanicallypulped (e.g., groundwood), chemically pulped (including but not limitedto the kraft and sulfite pulping processes), thermomechanically pulped,chemithermomechanically pulped, and the like. The mixtures of any subsetof the above mentioned or related fiber classes may be used.

In certain preferred embodiments the dispersible adhesively bonded wettissue laminates of the present invention comprise first and secondtissue plies, where each of the tissue plies are wet-laid tissue pliesand consist essentially of wood pulp fibers, particularly softwood kraftpulp fibers and more preferably Southern softwood kraft pulp fibers.

While in certain embodiments it may be preferable to form the tissueplies entirely from a single fiber type, such as softwood kraft pulpfibers, in other instances the plies may combine two or more fibertypes. For example, a headbox may be stratified to permit production ofa multilayered structure from a single headbox jet in the formation of aweb. In particular embodiments, the web is produced with a stratified orlayered headbox to preferentially deposit shorter fibers on one side ofthe web for improved softness, with relatively longer fibers on theother side of the web or in an interior layer of a web having three ormore layers. The web is desirably formed on an endless loop offoraminous forming fabric which permits drainage of the liquid andpartial dewatering of the web.

Generally, the laminates of the present invention do not containnonwoven materials such as meltblown, coform, airlaid, bonded-carded webmaterials, hydroentangled materials, spunlace materials, andcombinations thereof. Rather, the laminates are formed by adhesivelybonding wet-laid tissue webs in facing arrangement with one another,where each of the wet-laid tissue webs form a ply.

The laminates of the present invention generally comprise two, three orfour tissue plies by well-known wet-laid papermaking processes such as,for example, creped wet pressed, modified wet pressed, crepedthrough-air dried (CTAD) or uncreped through-air dried (UCTAD). Forexample, creped tissue webs may be formed using either a wet pressed ormodified wet pressed process such as those disclosed in U.S. Pat. Nos.3,953,638, 5,324,575 and 6,080,279, the disclosures of which areincorporated herein in a manner consistent with the instant application.In these processes the embryonic tissue web is transferred to a Yankeedryer, which completes the drying process, and then creped from theYankee surface using a doctor blade or other suitable device.

In other instances, the tissue plies are made by a through-air driedprocess known in the art. In such processes the embryonic web isnoncompressively dried. For example, textured tissue plies may be formedby either creped or uncreped through-air dried processes. Particularlypreferred are uncreped through-air dried webs, such as those describedin U.S. Pat. No. 5,779,860, the contents of which are incorporatedherein in a manner consistent with the present disclosure.

In still other instances the tissue plies may be manufactured by aprocess including the step of using pressure, vacuum, or air flowthrough the wet web (or a combination of these) to conform the wet webinto a shaped fabric and subsequently drying the shaped sheet using aYankee dryer, or series of steam heated dryers, or some other means,including but not limited to tissue made using the ATMOS processdeveloped by Voith or the NTT process developed by Metso; or fabriccreped tissue, made using a process including the step of transferringthe wet web from a carrying surface (belt, fabric, felt, or roll) movingat one speed to a fabric moving at a slower speed (at least 5 percentslower) and subsequently drying the sheet. Those skilled in the art willrecognize that these processes are not mutually exclusive, e.g., anuncreped TAD process may include a fabric crepe step.

The instant multi-ply tissue product may be constructed from two or moreplies that are manufactured using the same or different tissue makingtechniques. In a particularly preferred embodiment, the multi-ply tissueproduct comprises two or more plies, such as two, three or four plieswhere each of the plies comprise a wet-pressed tissue ply, and whereeach ply has a basis weight greater than about 10 gsm, such as fromabout 10 to about 45 gsm, such as from about 10 to about 42 gsm. In aparticularly preferred embodiment, each of the plies have substantiallysimilar basis weights and the upper most ply comprises a plurality ofmacrofolds.

Regardless of the tissue making process used to produce the individualplies, the resulting multi-ply tissue product comprises at least twoplies that are adhesively attached to one another by an ion triggerablebinder. In a particularly preferred embodiment both the first and secondtissue plies 20, 30 are wet-laid tissue plies and comprise softwoodkraft pulp fibers. In still other embodiments the first and secondtissue plies 20, 30 are through-air dried tissue plies consistingessentially of softwood kraft pulp fibers and having a basis weight fromat least about 10 gsm, such as from about 10 to about 60 gsm, such asfrom about 15 to about 45 gsm.

With reference now to FIG. 2 , the dispersible wet wipe 10 comprisesfirst and second plies 20, 30, which comprise a plurality of papermakingfibers 60. The plies 20, 30 each have an outer surface 22, 32 and anadhesive 40 disposed thereon. The outer surfaces 22, 32 are broughttogether in facing relation and bonded together by the adhesive 40 alongan interface 50.

In the illustrated embodiment an adhesive 40 has been applied as acoating to both of the outer surfaces 22, 32. In particular embodiments,the binder is applied as randomly distributed deposits binder on each ofthe outer surfaces. “Randomly distributed deposits” as used herein meansthat the elements of binder that form the coating are applied withoutany predetermined pattern, but are instead randomly applied in acontinuous, uninterrupted operation, such as via a continuous mistspray, a continuous rotary print coater, a continuous brush coater, orthe like. It is understood that at a microscopic level, the deposits ofbinder may have space between them; “randomly distributed deposits” ismeant to distinguish from, for example, an application having adistinct, predetermined, repeating pattern that is visible to the nakedeye.

One example of a random pattern 80 of adhesive 40 useful in the presentinvention is illustrated in FIG. 3 . The adhesive 40 may be applied in arandom pattern 80 to a first outer surface 22 of a tissue ply 20 by acontinuous, uninterrupted operation, such as via a continuous mistspray, a continuous rotary print coater, a continuous brush coater, orthe like.

In other embodiments the binder may be applied in a pattern on one ormore of the tissue ply outer surfaces. In a particularly preferredembodiment, the binder is applied in an intermittent pattern by rollprinting the binder onto the ply outer surface. “Intermittent” withrespect to a particular pattern means applied in a manner such thatregions that include the binder alternate with regions that don'tinclude the binder. In particular embodiments, the intermittent patternis a lattice pattern. Examples of suitable intermittent patterns includean acorn pattern, a honeycomb pattern, a bow-tie pattern, a hound'stooth pattern, a herringbone pattern, a chessboard pattern, and thelike.

Referring to FIG. 4 , an intermittent pattern 100 useful in the presentinvention is illustrated. The intermittent pattern 100 comprisescontinuous, optionally parallel, lines 102 of adhesive 40 that extend ina primarily cross-machine direction (CD). The pattern 100 furthercomprises intermittent portions 104 between the lines 102 that aresubstantially free from an adhesive.

With reference again to FIG. 2 , although the adhesive 40 is generallyapplied to the tissue ply outer surfaces 22, 32, the binder may disperseinto the tissue ply in the z-direction. The migration of the binder fromthe tissue ply surface into the interior of the ply is generally random,resulting in a non-uniform z-directional gradient of the adhesive withinthe tissue ply. While the z-directional gradient of the adhesive may berandom, in certain instances, the highest concentration of the adhesiveis located at the outer surface of the tissue ply. Further, the adhesivemay not migrate entirely throughout the z-direction of the tissue ply,but rather be located in proximity of the outer surface.

The percentage of the outer ply surface area that is treated with bindermay vary. “Binder surface area” as used herein means the area bounded bythe cumulative footprint upon which the binder is applied, withoutregard to the microscopic space between individual deposits of binder.In particular embodiments, the binder surface area is 100 percent of thefirst surface area. In other embodiments the binder surface area is atmost 75 percent, at most 50 percent, at most 25 percent.

Just as the surface area of the ply treated with binder may vary, theamount of binder applied to one or more of the tissue plies may alsovary. In certain embodiments, the amount of binder applied to one ormore of the tissue plies may be about 1.5 grams per square meter (gsm)or more, such as 2.0 gsm or more, such as about 4.0 gsm or more. Incertain embodiments, binder is applied to an outer surface of first andsecond tissue plies and the total binder add-on is from about 3.0 toabout 15 gsm, such as from about 4.0 to about 10 gsm.

In particularly preferred embodiments, the adhesive is a triggerablebinder. A variety of triggerable binders may be used. One type oftriggerable binder is a dilution triggerable binder. Examples ofdilution triggerable binders include ion-sensitive polymers, which maybe employed in combination with a wetting composition in which theinsolubilizing agent is a salt. Other dilution triggerable binders mayalso be employed, wherein these dilution triggerable binders are used incombination with wetting agents using a variety of insolubilizingagents, such as organic or polymeric compounds.

Although the triggerable binder may be selected from a variety ofpolymers, including temperature sensitive polymers and pH-sensitivepolymers, the triggerable binder may preferably be the dilutiontriggerable binder, comprising the ion-sensitive polymer. If theion-sensitive polymer is derived from one or more monomers, where atleast one contains an anionic functionality, the ion-sensitive polymeris referred to as an anionic ion-sensitive polymer. If the ion-sensitivepolymer is derived from one or more monomers, where at least onecontains a cationic functionality, the ion-sensitive polymer is referredto as a cationic ion-sensitive polymer. An exemplary anionicion-sensitive polymer is described in U.S. Pat. No. 6,423,804, which isincorporated herein in its entirety by reference.

Examples of cationic ion-sensitive polymers are disclosed in thefollowing U.S. Patent Application Publication Nos.: 2003/0026963,2003/0027270, 2003/0032352, 2004/0030080, 2003/0055146, 2003/0022568,2003/0045645, 2004/0058600, 2004/0058073, 2004/0063888, 2004/0055704,2004/0058606, and 2004/0062791, all of which are incorporated herein byreference in their entirety, except that in the event of anyinconsistent disclosure or definition from the present application, thedisclosure or definition herein shall be deemed to prevail.

Desirably, the ion-sensitive polymer may be insoluble in the wettingcomposition, wherein the wetting composition comprises at least about0.3 weight percent of an insolubilizing agent which may be comprised ofone or more inorganic and/or organic salts containing monovalent and/ordivalent ions. More desirably, the ion-sensitive polymer may beinsoluble in the wetting composition, wherein the wetting compositioncomprises from about 0.3 to about 3.5 percent by weight of aninsolubilizing agent which may be comprised of one or more inorganicand/or organic salts containing monovalent and/or divalent ions. Evenmore desirably, the ion-sensitive polymer may be insoluble in thewetting composition, wherein the wetting composition comprises fromabout 0.5 to about 3.5 percent by weight of an insolubilizing agentwhich comprises one or more inorganic and/or organic salts containingmonovalent and/or divalent ions. Especially desirable, the ion-sensitivepolymer may be insoluble in the wetting composition, wherein the wettingcomposition comprises from about 1 to about 3 percent by weight of aninsolubilizing agent which comprises one or more inorganic and/ororganic salts containing monovalent and/or divalent ions. Suitablemonovalent ions include, but are not limited to, Na+ ions, K+ ions, Li+ions, NH4+ ions, low molecular weight quaternary ammonium compounds(e.g., those having fewer than 5 carbons on any side group), and acombination thereof. Suitable divalent ions include, but are not limitedto, Zn2+, Ca2+ and Mg2+. These monovalent and divalent ions may bederived from organic and inorganic salts including, but not limited to,NaCl, NaBr, KCl, N H4Cl, Na2SO4, ZnCl2, CaCl2, MgCl2, MgSO4, andcombinations thereof. Typically, alkali metal halides are the mostdesirable monovalent or divalent ions because of cost, purity, lowtoxicity, and availability. A desirable salt is NaCl.

In a preferred embodiment, the ion-sensitive polymer may desirablyprovide the wipe substrate with sufficient in-use strength(typically >300 grams per linear inch) in combination with the wettingcomposition containing sodium chloride. These wipe substrates may bedispersible in tap water, desirably losing most of their wet strength(<200 grams per linear inch) in one hour or less.

In another preferred embodiment, the ion-sensitive polymer may comprisethe cationic sensitive polymer, wherein the cationic sensitive polymeris a cationic polyacrylate that is the polymerization product of 96 mol% methyl acrylate and 4 mol % [2-(acryloyloxy)ethyl]trimethyl ammoniumchloride.

In certain instances, the adhesive may comprise a triggerable binderand/or the cobinder. When the binder composition comprises thetriggerable binder and the cobinder, the triggerable binder and thecobinder may preferably be compatible with each other in aqueoussolutions to: 1) allow for facile application of the binder compositionto the fibrous substrate in a continuous process and 2) preventinterference with the dispersibility of the binder composition.Therefore, if the triggerable binder is the anionic ion-sensitivepolymer, cobinders which are anionic, nonionic, or very weakly cationicmay be preferred. If the triggerable binder is the cationicion-sensitive polymer, cobinders which are cationic, nonionic, or veryweakly anionic may be added. Additionally, the cobinder desirably doesnot provide substantial cohesion to the wipe substrate by way ofcovalent bonds, such that it interferes with the dispersibility of thewipe substrate.

The presence of the cobinder may provide a number of desirablequalities. For example, the cobinder may serve to reduce the shearviscosity of the triggerable binder, such that the binder compositionmay be more easily sprayed compared to the triggerable binder alone. Byuse of the term “sprayable” it is meant that these polymers may beapplied to the fibrous material or substrate by spraying, allowing theuniform distribution of these polymers across the surface of thesubstrate and penetration of these polymers into the substrate. Thecobinder may also reduce the stiffness of the wipe substrate compared tothe stiffness of a wipe substrate to which only the triggerable binderhas been applied. Reduced stiffness may be achieved if the cobinder hasa glass transition temperature (Tg), which is lower than the Tg of thetriggerable binder. In addition, the cobinder may be less expensive thanthe triggerable binder and by reducing the amount of triggerable binderneeded, may serve to reduce the cost of the binder composition. Thus, itmay be desirable to use the highest amount of cobinder possible in thebinder composition such that it does not jeopardize the dispersibilityand in-use strength properties of the wet wipe. In a preferredembodiment, the cobinder replaces a portion of the triggerable binder inthe binder composition and permits a given strength level to beachieved, relative to a wet wipe having approximately the same tensilestrength but containing only the triggerable binder in the bindercomposition, to provide at least one of the following attributes: lowerstiffness, better tactile properties (e.g. lubricity or smoothness), orreduced cost.

In one embodiment, the cobinder present in the binder composition,relative to the mass of the binder composition, may be about 10 percentor less, more desirably about 15 percent or less, more desirably 20percent or less, more desirably 30 percent or less, or more desirablyabout 45 percent or less. Exemplary ranges of cobinder relative to thesolid mass of the binder composition may include from about 1 to about45 percent, from about 25 to about 35 percent, from about 1 to about 20percent and from about 5 to about 25 percent.

The cobinder may be selected from a wide variety of polymers, as areknown in the art. For example, the cobinder may be selected from thegroup consisting of poly(ethylene-vinyl acetate),poly(styrene-butadiene), poly(styrene-acrylic), a vinyl acrylicterpolymer, a polyester latex, an acrylic emulsion latex, polyvinylchloride), ethylene-vinyl chloride copolymer, a carboxylated vinylacetate latex, and the like. A variety of additional exemplary cobinderpolymers are discussed in U.S. Pat. No. 6,653,406 and U.S. PatentApplication Publication No. 2003/00326963, which are both incorporatedherein by reference in their entirety. Particularly preferred cobindersinclude Airflex® EZ123 and Airflex® 110.

The wipe further includes a wetting composition. The wetting compositionmay include a first insolubilizing agent, and optionally a secondinsolubilizing agent. Desirably, the adhesive is insoluble (stable) inthe presence of the wetting composition containing one or moreinsolubilizing agents. In other words, the one or more insolubilizingagents render stable the adhesive, prior to the wipe being flushed intoa toilet or otherwise contacted by tap water. “Stable” as used hereinmeans continuing to hold the fibers of the wipe together as intended foruse of the wipe.

The liquid wetting composition can be any liquid that can be absorbedinto the wipe substrate and may include any suitable components thatprovide the desired wiping properties. For example, the solution mayinclude water, emollients, surfactants, fragrances, preservatives,organic or inorganic acids, chelating agents, pH buffers, orcombinations thereof, as are well known to those skilled in the art.Further, the wetting composition may also contain lotions, medicaments,and/or antimicrobials. The wetting composition may contain additionalagents that impart a beneficial effect on skin or hair and/or furtheract to improve the aesthetic feel of the compositions and wipesdescribed herein. Examples of suitable skin benefit agents includeemollients, sterols or sterol derivatives, natural and synthetic fats oroils, viscosity enhancers, rheology modifiers, polyols, surfactants,alcohols, esters, silicones, clays, starch, cellulose, particulates,moisturizers, film formers, slip modifiers, surface modifiers, skinprotectants, humectants, sunscreens, and the like.

The wetting composition may be incorporated into the wipe in an add-onamount of from about 10 to about 600 percent, more desirably from about100 to about 500 percent, and even more desirably from about 200 toabout 300 percent of the dry weight of the substrate. In one example,the wetting composition contains water. The wetting composition can inparticular embodiments contain water in an amount of from about 40 toabout 99 percent of the total weight of the solution.

In certain embodiments the dispersible wet wipe of the present inventionhas a cross-machine direction wet tensile strength (“CDWT”) of greaterthan 150 g/in, more particularly greater than 175 g/in, and moreparticularly great than 200 g/in, such as from about 150 to about 300g/in, such as from about 175 to about 250 g/in. Having a CDWT strengthin this range can help prevent the wipe from tearing during dispensingor during personal hygiene use.

In yet other embodiments adhesively bonding the tissue plies together toform a dispersible laminate provides the laminate with improved tensilestrength, particularly improved geometric mean wet tensile strength(GMWT). Desirably, the dispersible wet wipes have a GMWT strength of atleast about 250 g/in, such as at least about 275 g/in, such as at leastabout 300 g/in, such as from about 250 to about 500 g/in, such as fromabout 275 to about 400 g/in.

In particular embodiments, the wipe has a CDWT after soaking for 15minutes in room temperature tap water of less than 100 g/in, such asfrom about 50 to about 100 g/in. In other embodiments, the wipepreferably has a 60-min post-soak CDWT of less than 80 g/in, and morepreferably less than 65 g/in. Having a post-soak CDWT in this rangebears on the wipe's ability to lose strength and break down inwastewater conveyance infrastructure after flushing, as the minimum timethat a wipe would reside in a home drain line after being flushed is 15minutes (although typically wipes reside in the home drain line longerthan 15 minutes).

In still other embodiments, the present invention provides a dispersiblewipe comprising two or more wet-laid tissue layers adhesively bonded toone another having a CDWT of greater than 200 g/in, more particularlygreater than 225 g/in, and more particularly great than 250 g/in, and aSlosh-Box Break-Up Time of less than about 60 minutes, more particularlyless than about 45 minutes, and more particularly less than about 30minutes, in accordance with the test procedure set forth below.

In a particularly preferred embodiment the present invention provides adispersible wipe comprising two or more wet-laid tissue layersadhesively bonded to one another and comprising wood pulp fibers andfrom about 2 to about 10 grams per square inch adhesive disposed betweenthe layers, the product having a GMWT from about 275 to about 400 g/inand a Slosh Time less than about 30 minutes, such as from about 2 toabout 30 minutes, such as from about 5 to about 20 minutes.

Turning now to FIG. 5 , one method of manufacturing a wipe according tothe present invention is illustrated. The method includes providingfirst and second tissue webs 101, 103. Each web having an outer surface105, 107. In certain instances, the webs may have a basis weight fromabout 10 to about 60 gsm, such as from about 15 to about 40 gsm and morepreferably from about 20 to about 35 gsm.

An adhesive solution 110 is pumped into a reservoir or doctor chamber112 and then applied onto antilox roll 114 by doctor chamber 112 usingtwo doctor blades that keep the doctor chamber 112 sealed. Antilox roll,used in certain embodiments of the present invention, is made by placinga coating (approximately 0.020 inches thick in some cases) of chromiumoxide on the outer perimeter of a round steel roll. The chromium oxidemay then be etched with a laser. The laser burns microscopic gravurecells onto the surface of the chromium oxide. The cells fill up withadhesive 110 as the roll 114 is rotated.

The adhesive 110 is mechanically transferred from the anlilox roll 114onto flexographic printing roll 116, which may be a rubber flexographicprinting roll. A specific metered amount of the adhesive 110 is thentransferred, due to capillary forces, out of the gravure cells onantilox roll 114 and onto flexographic printing roll 116. Thisflexographic printing roll 116, which may have an engraved pattern onits surface, contacts the outer surface 107 of the second web 103 as theweb 103 passes through a nip 118 created by the flexographic printingroll 116 and a backing roll 120. As the web 103 passes through the nip118 the adhesive 110 is applied to its outer surface 107.

This second web 103, now containing the adhesive 110 on its outersurface 107 is met by untreated first tissue web 101, and the two webs101, 103 are adhesively joined in a facing arrangement by passingthrough a second nip 122 formed between the backing roll 120 and amarrying roll 124. The two-ply, adhesively bonded, product 130 may befurther converted in additional processes. Thus, the present inventionproduces a dispersible tissue product comprising two tissue plieswherein the adhesive is between the layers and not on the exterior as inknown products.

For ease of application, the adhesive may be dissolved in water, or in anon-aqueous solvent, such as methanol, ethanol, acetone, or the like,with water being the preferred solvent. The amount of binder dissolvedin the solvent may vary depending on the polymer used and theapplication method. Desirably, the adhesive solution contains less thanabout 18 percent by weight of adhesive composition solids. Moredesirably, the adhesive solution contains less than 16 percent by weightof adhesive composition solids.

In alternative embodiments of the present invention, such as thatillustrated in FIGS. 6 and 7 , the adhesive may be applied to the outersurfaces of one or more of the tissue plies by spraying. For example,with reference to FIG. 6 , individual tissue webs 101 and 103 areunwound from the reel stands and threaded over carrier rolls 141, 142.First and second spray assemblies 151, 153 are positioned betweencarrier rolls 141, 142 and a nip 155 created by opposed first and secondrolls 161, 163. The spray assemblies 151, 153 are further positionedbeneath, and across the width of (i.e. transverse to the movement of)each of the individual tissue webs 101 and 103 to spray an adhesive 110to an outer surface 105, 107 of each web 101, 103.

The spray assemblies may include a row of nozzles positioned in ahousing which extends across the width of the web. Nozzles may be spacedapart from one another to provide the desired degree of coverage and incertain instances may be positioned such that any given point on the webgenerally receives output from two nozzles. Each nozzle is generallyconnected to an adhesive supply and atomizing air supply and a controlair supply. The housing may include an axle that extends across thewidth of the housing and controls the rotation of a baffle plate. Thehousing may also include a trailing lip extending from the rear(trailing) edge.

After adhesive 110 is sprayed onto the outer surface 105, 107 of eachweb 101, 103, the webs are combined in facing arrangement as they passthrough a nip 155. The nip 155 may be formed by a pair of opposed rolls161, 163, which in certain instances may be urged against one another toapply a pressure to the nip. Formation of nips in this manner is commonin the converting of tissue products and generally, it is desirable toload these rolls to one another at a set force. One of skill in the artwill recognize this to be known generally as the nip force and isgenerally provided (or referenced) in terms of force per unit length. Byconvention herein, the units are known as pounds per linear inch (PLI orpli). In certain embodiments the force observed between the pair ofopposed rolls 161, 163 is at least about 5 pli, such as from about 5 toabout 60 pli, such as from about 10 to about 40 pli.

The adhesive 110 applied by the first and second spray assemblies 151,153 may have the same chemical composition, and perhaps even the samelevel of concentration prior to application. In other embodiments thechemical composition of the adhesives is different, and they are appliedat different add-on levels. In still other embodiments, adhesive 110applied by the first and second spray assemblies 151, 153 may be appliedin the same pattern or may be applied in different patterns to the outersurface 105, 107 of each web 101, 103.

There can be advantages to applying the first and second binders in twoseparate steps and by two different application techniques. Withoutwishing to limit the scope of the invention, it is believed that byapplying one stage of binder in a low-level, “all over” coating, andanother stage of binder in a pattern having repeating gaps therein, anoptimal balance between in-use strength and good post-flushdispersibility can be struck.

In other embodiments, such as that illustrated in FIG. 7 , the laminate180 is produced using a single spray assembly 151 that is positioned toapply adhesive 110 to the outer surfaces 105, 107 of each web 101, 103immediately prior to a nip 155. Individual tissue webs 101 and 103 areunwound from the reel stands and threaded over carrier rolls 141, 142.The single spray assembly 151 is positioned between the carrier rolls141, 142 and the nip 155 to spray adhesive 110 onto the outer surfaces105, 107. After adhesive 110 is sprayed onto the outer surface 105, 107of each web 101, 103, the webs are combined in facing arrangement asthey pass through a nip 155.

After the plies are attached in facing arrangement by passing theadhesively treated webs 101, 103 through the nip 155, the multi-plyadhesively bonded laminate 180 may be wound into a roll and/or subjectedto further treatment or converting.

In one particularly preferred embodiment, multi-ply adhesively bondedlaminate is conveyed through a dryer to cure the adhesive. In certaininstances, the multi-ply adhesively bonded laminate may be transferredto a through-air dryer fabric and conveyed over a through-air dryer todry the laminate and/or cure the adhesive. In some embodiments, thethrough-drying fabric is a course, highly permeable, fabric. Inalternative embodiments, other methods may be used as a substitute for,or in conjunction with, the through-air dryer to dry the laminate and/orcure the adhesive. For example, in some embodiments the through-airdryer may be used without a fabric. In other suitable embodiments of thedisclosure, other drying systems known in the art (i.e., other than athrough-air dryer system, e.g., drying cans, infra-red (IR), ovens) maybe used so long as they do not deviate from the scope of thisdisclosure.

When using an ethylene vinyl acetate copolymer adhesive, the dryingapparatus can be heated to a temperature of between about 120 to about170° C.

The dried and/or cured laminate may be wound into a roll or reel. Afterwinding, subsequent converting steps known to those of skill in the artcan be used to transform the textured air laid substrate into aplurality of wet wipes. For example, the textured air laid substrate canbe cut into individual wipes, the individual the wipes folded into astack, the stack of wet wipes moistened with a liquid wettingcomposition, and then the stack of wet wipes can be placed into adispenser.

Test Methods

Tensile Strength

For purposes herein, tensile strength may be measured using a ConstantRate of Elongation (CRE) tensile tester using a 1-inch jaw width (samplewidth), a test span of 3 inches (gauge length), and a rate of jawseparation of 25.4 centimeters per minute after maintaining the sampleat the ambient conditions of 23±2 degrees Celsius and 50±5 percentrelative humidity for four hours before testing the sample at the sameambient conditions. The wet wipes are cut into 1-inch wide by 5.5 incheslong strips cut from the center of the wipes in the cross-machinedirection (CD) orientation. The “cross-machine direction wet tensilestrength” (“CDWT”) is the peak load in grams-force per inch of samplewidth when a specimen is pulled to rupture in the cross-machinedirection.

The instrument used for measuring tensile strength was an MTS SystemsSinergie 200 model. The data acquisition software was MTS TestWorks® forWindows Ver. 4.0 commercially available from MTS Systems Corp., EdenPrairie, Minn. The load cell was an MTS 50 Newton maximum load cell. Thegauge length between jaws is 3 inches. The top and bottom jaws areoperated using pneumatic-action with maximum 80 P.S.I. The breaksensitivity is set at 40 percent. The data acquisition rate is set at100 Hz (i.e., 100 samples per second). The sample is placed in the jawsof the instrument, centered both vertically and horizontally. The testis then started and ended when the force drops by 40 percent of peak.The peak load expressed in grams-force is recorded as the “CDWT” of thespecimen. Eight representative specimens were tested for each productand the average peak load determined.

To simulate post-flush tensile strength measurements, five specimens areflushed down a toilet with water at room temperature, allowed to rest inthe drain line for 15 or 60 minutes, and then measured for CDWT asdescribed above.

Dispersibility

This test method evaluates the dispersibility of flushable consumerproducts, simulating travel through a wastewater conveyance system(“Slosh Box Test”). In this test method, a plastic tank is loaded with aproduct and 2 liters of tap water at room temperature. The container isthen tipped back and forth at 26 oscillations per minute to simulate themovement of wastewater in the collection system. The time required forthe wipe specimen to break up entirely into pieces that measure at mostapproximately 1 sq. in. (6.5 sq. cm) is recorded. The amount of time toreach this point is measured (“Slosh-Box Break-Up Time”). Theconstruction and motion of the apparatus is conducted as set forth inthe “Guidelines for Assessing the Flushability of Disposable NonwovenProducts, Third Edition, FG502—Slosh Box Disintegration Test,” availablefrom the “Association of the Nonwovens Fabrics Industry,” 1100 CrescentGreen, Suite 115, Cary, N.C., 27518, www.inda.org.

Examples

Each of the samples, control and inventive, comprise one or moreuncreped through-air dried (“UCTAD”) tissue plies. Each of the UCTADplies are formed from a fiber furnish consisting essentially of bleachedNorthern softwood kraft (NSWK) fibers. The number of plies and theirrespective basis weights for the control and inventive sample are setforth in Table 1, below.

TABLE 1 Target Ply Basis Weight Sample Number of Plies (gsm) Control 148 Inventive 2 Ply 1-25 gsm Ply 2-35 gsm

The inventive samples were made using adhesive comprising a triggerablebinder composition having both a binder and a cobinder. The binder wascationic polyacrylate which is the polymerization product of 92 mol %methyl acrylate, 4 mol % hydroxypropyl acrylate and 4 mol %[2-(acrylolyoxy)ethyl] trimethyl ammonium chloride. The cobinder wasVINNAPAS® EZ123, available from Wacker Chemi AG. The binder and thecobinder, both supplied in solution, were mixed together to yield a70:30 binder to cobinder dry-weight ratio.

The inventive dispersible laminate was prepared by unwinding a firsttissue ply and applying the triggerable binder composition to an outersurface by spraying. The triggerable binder composition was sprayedusing a single Unijet® spray nozzle, Nozzle type 800017, manufactured bySpraying Systems Co., Wheaton, Ill., operating at 80 psi. Thetriggerable binder composition (in aqueous solution at 15.5 percent) wassprayed onto the outer surface of a first tissue ply to yield anadhesive dry solids basis weight of 4 grams per square meter.

After being sprayed with the triggerable binder composition, the firsttissue ply was brought into facing relation with the second tissue plyand passed through a nip to form an adhesively bonded two-ply laminate.The two-ply laminate was passed through a calender nip loaded at apressure of 12 pli and then passed through a series of dryers comprisinga through-air dryer and an infra-red dryer operating from about 220 to260° C. at a speed of about 200 feet per minute (fpm) to dry the web.The dried web was then passed through the same series of driers a secondtime at a speed of about 100 to about 200 fpm to cure the binder.

A control wet wipe was prepared by unwinding a single ply of UCTAD webhaving a basis weight of about 48 gsm and applying the triggerablebinder composition to an outer surface by spraying. The triggerablebinder composition was sprayed using a single Unijet® spray nozzle,Nozzle type 800017, manufactured by Spraying Systems Co., Wheaton, Ill.,operating at 80 psi. The triggerable binder composition (in aqueoussolution at 15.5 percent) was sprayed onto the outer surface of a firsttissue ply to yield an adhesive dry solids basis weight of 4 grams persquare meter.

After being sprayed with the triggerable binder composition, the web wasdried through a series of dryers comprising a through-air dryer and aninfra-red dryer operating from about 220 to 260° C. at a speed of about200 feet per minute (fpm) to dry the web. The dried web was then passedthrough the same series of driers a second time at a speed of about 100to about 200 fpm to cure the binder.

A wetting composition was added to both the control and inventive wipesat an add-on rate of 215 percent of the weight of the dry wipe, and thewetting composition comprised 2 weight-percent of sodium chloride. Thewetted web was converted into stacks of wipes and stored inmoisture-impervious plastic bags.

For each sample, five specimens, roughly 2.5 centimeters by 14centimeters in dimension, were tested for CDWT, in units of grams perlinear inch, and additional specimens were tested for CDWT after beingsoaked for sixty (60) minutes in tap water at room temperature, andresults averaged. The cross-machine direction wet tensile strength wasmeasured because in certain dispensing formats, the extraction forceplaced upon the wipe during dispensing is in the cross-machinedirection. The 60-minute soak was intended to simulate the time that awipe typically resides in a home drain line after being flushed.

The time required for each wipe to break apart into pieces, none ofwhich were larger than approximately one square inch (6.5 squarecentimeters), was measured via the Slosh-Box test described above.

TABLE 2 Control Inventive Adhesive Add-on (qsm)  4  4 Bone-Dry Basis Wt.(qsm)  48  59.1 CDWT (q/in) 211 185 MDWT (g/in) 424 387 GMWT (g/in) 299268 CDWT Strength 1 hr Soak  31  22 Strength Loss after 1 hr Soak (%) 85%  88% Slosh Box Break-Up Time (min)  66.5  17.8

Embodiments

First embodiment: A dispersible adhesively bonded wet tissue laminatecomprising: a first tissue ply and a second tissue ply, each ply havinga first outer surface and a second outer surface, the first and secondplies arranged in facing relation with one another such that the secondouter surfaces face one another; an adhesive disposed between the firstand second tissue ply second outer surfaces; and a wetting composition.

Second embodiment: The laminate of the first embodiment wherein thetissue laminate has a geometric mean wet tensile strength (GMWT) greaterthan about 250 g/in and a Slosh Time less than about 60 minutes.

Third embodiment: The laminate of the first or second embodiment whereinthe first and second tissue plies are wet-laid tissue plies.

Fourth embodiment: The laminate of any one of the first through thirdembodiments wherein the first and second tissue plies are wet-laidtissue plies having a basis weight from about 10 to about 60 grams persquare meter (gsm).

Fifth embodiment: The laminate of any one of the first through fourthembodiments wherein the first and second tissue plies are wet-laid andthrough-air dried tissue plies having a basis weight from about 10 toabout 30 gsm.

Sixth embodiment: The laminate of any one of the first through fifthembodiments wherein the first and second tissue plies are substantiallyidentical.

Seventh embodiment: The laminate of any one of the first through sixthembodiments wherein the first and second tissue plies differ in at leastbasis weight, fiber composition, or geometric mean tensile strength.

Eighth embodiment: The laminate of any one of the first through seventhembodiments wherein the tissue laminate has a cross-machine directionwet tensile strength (CDWT) greater than about 150 g/in.

Ninth embodiment: The laminate of any one of the first through eighthembodiments wherein the tissue laminate has a GMWT from about 175 toabout 300 g/in, a CDWT from about 150 to about 250 g/in, and a SloshTime less than about 20 minutes.

Tenth embodiment: The laminate of any one of the first through ninthembodiments wherein the adhesive add-on ranges from about 2.0 to about10 gsm.

Eleventh embodiment: The laminate of any one of the first through tenthembodiments wherein the wetting composition add-on amount ranges fromabout 10 to about 600 percent by weight of the dry tissue laminate andthe wetting composition comprises water and from about 0.4 and about 3.5percent, by weight of the wetting composition, of an insolubilizingagent. In certain embodiments the insolubilizing agent comprises aninorganic salt or an organic salt.

Twelfth embodiment: The laminate of any one of the first througheleventh embodiments wherein the adhesive is a triggerable bindercomposition and is added at an add-on rate of between about 1 and about4 percent based on the total weight of the dry laminate.

Thirteenth embodiment: The laminate of any one of the first throughtwelfth embodiments wherein the basis weight of the first and the secondtissue plies ranges from about 20 to about 80 grams per square meter.

Fourteenth embodiment: The laminate of any one of the first throughthirteenth embodiments wherein the first and second tissue pliescomprise an uncreped through-air dried tissue web.

Fifteenth embodiment: The laminate of any one of the first throughfourteenth embodiments wherein the laminate does not comprise an airlaidnonwoven layer.

What is claimed is:
 1. A method of making a dispersible adhesively bonded wet tissue laminate: (a) providing a first wet-laid tissue web having a first surface and a second surface; (b) providing a second wet-laid tissue web having a first surface and a second surface; (c) applying an adhesive to the first surface of the first wet-laid tissue web; (d) after applying the adhesive to the first surface bringing the first surface into facing relation with the first surface of the second wet-laid tissue web; (e) passing the first and second wet-laid tissue webs through a nip to form and adhesively bonded tissue laminate; and (f) applying a wetting composition wetting composition to the adhesively bonded tissue laminate, wherein the add-on amount of the wetting composition ranges from about 10 to about 600 percent by weight of the dry adhesively bonded tissue laminate.
 2. The method of claim 1 wherein the wet adhesively bonded tissue laminate has a geometric mean wet tensile strength (GMWT) greater than about 250 g/in and a Slosh Time less than about 60 minutes
 3. The method of claim 1 further comprising the step of applying a second binder to the first surface of the second wet-laid tissue web.
 4. The method of claim 3 wherein the first and second binders are the same.
 5. The method of claim 3 wherein the first and second binders are sprayed onto the first surfaces.
 6. The method of claim 3 wherein the first binder is sprayed onto the first surface and wherein the second binder is not sprayed onto the first surface.
 7. The method of claim 3 wherein the second adhesive is roll-printed onto the first surface.
 8. The method of claim 1 further comprising heat curing the laminate.
 9. The method of claim 1 wherein the first and second tissue plies are through-air dried tissue plies having a basis weight from about 10 to about 30 gsm.
 10. The method of claim 1 wherein the adhesive add-on ranges from about 2.0 to about 10 gsm.
 11. The method of claim 1 wherein the adhesive is a cationic polyacrylate.
 12. The method of claim 1 wherein the adhesive is a cationic polyacrylate and further comprises a cobinder selected from the group consisting of poly(ethylene-vinyl acetate), poly(styrene-butadiene), poly(styrene-acrylic), a vinyl acrylic terpolymer, a polyester latex, an acrylic emulsion latex, polyvinyl chloride), ethylene-vinyl chloride copolymer, and a carboxylated vinyl acetate latex.
 13. The method of claim 1 further comprising applying a vinyl-acetate ethylene latex cobinder to first surface of the first wet-laid tissue web. 